The present invention generally relates to thickened acid gels and uses for such thickened gels. For example, acid thickened solutions can be usefully employed in cleaning formulations such as hard surface cleaners, toilet bowl cleaners, industrial cleaners, and the like and in oilfield applications such as well stimulation. These and other uses will be apparent to the skilled artisan.
The compositions of the present invention are particularly useful in oilfield applications. Hydrocarbons are obtained by drilling a well that penetrates a subterranean hydrocarbon-bearing formation providing a partial flowpath for the oil to reach the surface. In order for oil travel from the formation to the wellbore there must be a flowpath from the formation to the wellbore. This flowpath is through the formation rock and has pores of sufficient size and number to allow a conduit for the oil to move through the formation.
A common reason for a decline in oil production is damage to the formation that plugs the rock pores and impedes the flow of oil to the wellbore and ultimately to the surface. This damage generally arises from deliberately injecting another fluid into the wellbore. Even after drilling, some drilling fluid remains in the region of the formation near the wellbore, which may dehydrate and form a coating on the wellbore. The natural effect of this coating is to decrease the permeability to oil moving from the formation in the direction of the wellbore.
Another reason for a decline in oil production occurs when the pores of the formation are small in size such that oil migrates toward the wellbore only very slowly. In both circumstances, it is desirable to improve the low permeability of the formation.
Well stimulation refers to the various techniques employed to improve the permeability of a hydrocarbon-bearing formation. Three general well-stimulation techniques are typically employed. The first involves injecting chemicals into the wellbore to react with and dissolve permeability damaging materials such as wellbore coatings. A second method requires injecting chemicals through the wellbore and into the formation to react with and dissolve small portions of the formation thereby creating alternative flowpaths for the hydrocarbons to flow to the wellbore. These alternative flow paths redirect the flow of oil around the low permeability or damaged areas of the formation. A third technique, often referred to as fracturing, involves injecting chemicals into the formation at pressures sufficient to actually fracture the formation, thereby creating a large flow channel though which hydrocarbon can more readily move from the formation and into the wellbore.
In one embodiment, the present invention is directed to methods to enhance the productivity of hydrocarbon bearing formations by removing near-wellbore formation damage or by creating alternate flowpaths by dissolving small portions of the formation. This is conventionally known as matrix acidizing. In this technique, acids, or acid-based fluids, are useful in this regard due to their ability to dissolve both formation minerals and contaminants which were introduced into the wellbore/formation during drilling or remedial operations. The primary fluids used in acid treatments are mineral acids such as hydrochloric acid which is still the preferred acid treatment in carbonate formations. For sandstone formations, the preferred fluid is a hydrochloric/hydrofluoric acid mixture.
The purpose of an acid treatment is to remove formation damage along as much of the hydrocarbon flow path as possible. An effective treatment must therefore remove as much damage as possible along the entire flow path. The fluids and techniques of the present invention allow maximum penetration of the acid resulting in a more effective treatment.
The thickened acid viscoelastic fluids of the present application also have applications in hydraulic fracturing, in gravel packing and in other well stimulation techniques known to one of ordinary skill in the art. Additionally, the acid thickened fluids of the present invention can usefully be employed in various household and industrial cleaners including, but not limited to, detergent compositions, toilet bowl cleaners, hard surface cleaners, grease cutting compositions, and the like.